Fatty Acid Metabolism Flashcards
Why are triacylglycerols great energy stores?
- They are highly reduced. Oxidation yields ~38 kJ/g (vs. 17 kJ/g for carbohydrates)
- They are nearly anhydrous, stored in virtually water-free droplets vs. 2 kJ/g for glycogen
All together, this results in ~6x more energy than glycogen for each gram of fat
What are the steps of fatty acid utilization?
- Mobilization: adipose tissue –> energy-requiring tissue
- Activation/transport: into mitochondria for degradation
- β-oxidation: stepwise breakdown to acetyl-CoA
How are fatty acids mobilized?
adipose tissue –> bloodstream
- lipolysis by hormones such as epinephrine and glucagon
- via Gs to stimulate triacylglycerol release
- hormone-sensitive lipase yields free fatty acids
- released into blood stream!
How are fatty acids carried into the tissues they need to reach?
serum albumin
They bind serum albumin which can bind up to 10 fatty acids per molecule and act as a carrier for their transport
Where does fatty acid oxidation take place?
mitochondrial matrix (like the TCA cycle)
How are fatty acids activated and when?
- fatty acyl-CoA synthetase (standard free energy = -34 kJ/mol)
- fatty acid attacks ATP, generating AMP and PPi
- CoA-SH attacks the carbonyl and AMP comes off, leaving fatty acyl-CoA
How oes fatty acyl-CoA get across the inner mitochonrial membrane?
The carnitine shuttle
- carnitine acyltransferase I replaces CoA with carnitine
- transporter shuttles fatty acyl-carnitine across inner membrane into matrix
- regenerate fatty acyl-CoA and carnitine using carnitine acyltransferase II
- carnitine returned to intermembrane space in exchange for fatty acyl-carnitine
What are the steps of β-oxidation?
Saturated fatty acyl-CoA degraded by four reactions:
- oxidation by FAD
- hydration
- oxidation by NAD+
- thiolysis
chain shortene by two carbons, generate FADH2, NADH, acetyl-CoA
What happens in fatty acid catabolism for fatty acids with an odd number of carbons?
Additional steps are required.
One succinyl-CoA is yielded via propionyl-CoA
When are additional steps required for fatty acid catabolism?
- double bonds (unsaturated fatty acids)
- odd number of carbones
- branced fatty acids
What is necessary for the breakdown of unsaturated fatty acids?
isomerase and sometimes reductase
What is the net ATP yield for breakdown of palmitoyl-CoA?
108.
Know how to do this calculation.
What happens at the end of one round of β-oxidation?
The shortened acyl-CoA undergoes another round…
What are the products of β-oxidation?
- fatty acyl-CoA, two carbons shorter than at the start
- acetyl-CoA
Where does fatty acid synthesis take place?
The cytosol
What are intermediates attached to during fatty acid synthesis?
acyl carrier protein
What are intermediates attached to during fatty acid breakdown?
CoA
What is the reductant in fatty acid synthesis?
NADPH
What are the oxidants in fatty acid degradation?
NAD+ and FADH2
How is malonyl-CoA synthesized?
From acetyl-CoA and bicarbonate by acetyl-CoA carboxylase with the use of biotin
What drives the process of fatty acid synthesis?
decarboxylation of malonyl-CoA which allows the remaining two carbons to attach to the acetyl group
What does each round of fatty acid synthesis consume?
one malonyl-CoA, two NADPH, releases one CO2
When does fatty acid synthesis stop?
With palmitate
Where does NADPH come from for fatty acid synthesis?
pentose phosphate pathway
converting malate to pyruvate with malic enzyme
